The Ion Mobility Spectrometer was invented by Dr. Martin J. Cohen and others in the late 1960's at Franklin GNO Corporation in West Palm Beach. The genesis of this idea resulted from Dr. Cohen's interest in gaseous electronics and radiation physics. The original patent for IMS, U.S. Pat. No. 3,699,333 was filed in October 1968, and granted Oct. 17, 1972. This patent discloses the concept of “Plasma Chromatography”, an early name for IMS and describes the instrument concept and shows a spectrum. This patent was followed by a number of others that describe refinements and expansions of the original IMS concept and instrument design, and discuss a variety of applications and analytical methodologies. These patents, all assigned to Franklin GNO, are: U.S. Pat. Nos. 3,593,018; 3,621,239; 3,621,240; 3,624,389; 3,626,178; 3,626,179; 3,626,180; 3,626,181; 3,626,182; 3,629,574; 3,668,382; 3,668,383; 3,668,385; 3,697,748; and 3,697,749. U.S. Pat. No. 3,845,301 granted Oct. 29, 1974, describes the design and functioning of an IMS very similar to those used to the current day, with the exception of the specific method of detecting and observing the ion peaks.
IMS has military and anti-terror utilities for the detection of chemical warfare (CW) agents and explosives, for which the instantly disclosed device is uniquely capable. The US and UK governments have purchased instruments for use in the area of CW agent detection, in particular.
Under government supported contract research, primarily for the FAA for explosives detection, and for NASA for a unique methodology using IMS for planetary atmosphere analyses, basic technology currently used at airports for trace vapor detection of concealed explosives was developed. The NASA work produced instrumentation that was capable of providing trace component analysis of the atmospheres of Mars, Titan, and comets. This methodology was commercialized for the analysis of ultra-high purity gases for the semiconductor industry.
Patents for an explosive detection application and for the pure gas analysis application were issued: U.S. Pat. No. 5,162,652 granted Nov. 10, 1992, and U.S. Pat. No. 5,457,316 granted Oct. 10, 1995. A number of pure gas analysis patents, both US and international, have been issued, e.g. U.S. Pat. No. 6,740,873 issued May 25, 2004, and U.S. Pat. No. 6,895,339 issued May 17, 2005. The instant inventors have targeted commercial and government applications that require a rugged, dependable, miniature Ion Mobility Spectrometer. The initial objective was to concentrate on the explosive detection market which provides the greatest opportunity for the instantly disclosed unique miniaturized IMS. The instant inventors developed a hand-held detector for trace explosives detection. However, the focus of the NASA SBIR was to continue the application of IMS for planetary atmosphere analysis in which the rugged hermetically sealed miniaturized design was important to reduce weight and consumables usage. Out of this work, another important prototype commercial application for pure gas analysis has also been developed.
U.S. Pat. No. 3,593,018, issued to Cohen on Jul. 13, 1971 is directed towards an apparatus and method for sorting and detecting ions in a drift cell, the electric fields applied to the cell being controlled at appropriate times to minimize dispersion of bunched ions produced by a pulsed source. Bunched product ions produced by ion-molecule reactions are analyzed in accordance with their velocity in a drift field.
U.S. Pat. No. 3,621,239, issued to Cohen on Nov. 16, 1971 deals with methods for sorting and detecting trace gases which undergo ion-molecule reactions. Particular species of reactant ions are selected by choice of reagent gas and/or by reactant ion filtering to produce predictable product ions by reaction with trace gas molecules of a sample. The sample may be reacted with different species of reactant ions and the results compared to confirm the presence of particular species of product ions. The reagents producing different species of reactant ions may have ionization potentials above and below the ionization potential of the expected trace gas molecules.
U.S. Pat. No. 3,624,389 issued to Cohen et al. on Nov. 30, 1971, is directed toward an apparatus and methods for sorting and detecting trace gases which undergo ion-molecule reactions. Positive or negative ions of the trace gas are formed by ion-molecule reactions between the molecules of the trace gas and primary ions from another gas. Ions are classified in accordance with their velocity in a stream of gas while subjected to an electric drift field.
U.S. Pat. No. 3,626,180 issued to Carroll et al. on Dec. 7, 1971, is directed towards apparatus and methods for sorting and detecting trace gases which undergo ion-molecule reactions, trace ions being formed in a reactive gaseous medium and being analyzed in a nonreactive gaseous medium. The ions are classified in accordance with their velocity in an electric drift field.
U.S. Pat. No. 3,626,182 issued to Cohen on Dec. 7, 1971, and is directed towards an apparatus and method for sorting and detecting ions in a drift cell, the electric fields applied to different regions of the cell being controlled at appropriate times to ensure the rapid withdrawal of the ions from a reaction region to an analysis region, the bunching of the ions in the analysis region, and thereafter the separation of the bunched ions in accordance with ion drift velocity, and detection of separated ion species.
U.S. Pat. No. 3,629,574 issued to Carroll on Dec. 21, 1971, deals with a process wherein electrons are separated from ions by subjecting these charged particles to a drift field to cause them to move from a first region toward a second region and by interposing an electron filter in the drift field between said regions, the filter comprising a pair of grid members to which high-frequency alternating voltages are applied. This principle is applied to an electron capture detector and to a device which separates and detects ions in accordance with their mobility.
U.S. Pat. No. 3,697,748 issued to Cohen on Oct. 10, 1972 is directed toward a process wherein response time of drift-cell apparatus for measuring trace gases is improved by heating the drift cell walls and/or the sample inlet to reduce the accumulation of sample substances. Heated filters and electrode structures with tortuous gas paths are also disclosed.
U.S. Pat. No. 3,697,749 issued to Wernlund on Oct. 10, 1972, is directed toward detection of small-source plumes, as by an airborne instrument, wherein ions formed from the molecules of a gaseous sample and collected by the airborne instrument are segregated in a drift field, and signals produced in response to the detection of the segregated ions are separated into short-duration plume signal components and long-duration background components. The short-duration components are indicated with enhanced resolution.
U.S. Pat. No. 3,699,333 issued to Cohen et al. on Oct. 17, 1972, is directed towards an apparatus and method for sorting and detecting trace gases which undergo ion-molecule reactions. Positive or negative ions of the trace gas are formed by ion-molecule reactions between the molecules of the trace gas and primary ions from another source. Ions are classified by selective ion gating according to their velocity in an electric drift field.
U.S. Pat. No. 3,845,301 issued to Wernlund et al. on Oct. 29, 1974, is directed toward a process wherein plasma chromatograph response time is decreased by improvement of the gas low. An ion-molecule reaction region is provided in tandem with a larger diameter drift region, and a gas outlet is provided at the junction of the regions. Sample gas flowing through the ion-molecule reaction region into the drift region is re-directed by a counter-low of drift gas through the drift region, causing both gases to exit through the outlet and reducing intrusion of the sample gas into the drift region. Diffuse gas flow is employed in both regions, special structures being provided to avoid gas jetting.
U.S. Pat. No. 4,855,595 issued to Blanchard on Aug. 8, 1989, discloses an ion mobility spectrometer for detecting ions and for facilitating controlled chemical reactions is described incorporating an inlet for carrier and sample gas, a reaction region having an ionization source and at least two electrodes for generating an electric field and a drift region having at least two electrodes for generating an electric field therein wherein each electrode is coupled to a power supply for placing a predetermined potential on the electrode and wherein each power supply is controlled by an electric field controller for providing a sequence of potentials on each electrode in the reaction region and drift region to control the motion and position of ions in the drift region. The invention claims to overcome the problem of detection sensitivity, detection selectivity and resolution between ions of similar mobility; however enablement of a gridless system is neither taught nor disclosed.
In a later published paper entitled “Ion Injection Mobility Spectrometer Using Field Gradient Barriers, i.e. Ion Wells (Blanchard et al, IJIMS 5(2002)3, Pp 15-18), a gridless system is disclosed. Blanchard requires the use of a dual zone system for creating a “Trigger well” and a “Storage Well” which must manipulate the voltages at two rings in order to provide an ion reservoir.
These disclosures further illustrate the inability of skilled artisans such as Blanchard and his colleagues to constructively or actually reduce to practice a miniaturized IMS device having highly enhanced sensitivity and performance for the detection of trace chemicals, particularly the relatively high molecular weight, low vapor pressure explosive chemicals.
U.S. Pat. No. 5,162,652 issued to Cohen et al. on Nov. 10, 1992, is directed towards an apparatus and method for the detection and identification of the presence of chosen molecules, typically toxic or contraband located within sealed luggage and the like, comprises subjecting the sealed luggage to a process whereby a portion of the enclosed atmosphere within the luggage is extracted and combined with the surrounding atmosphere in a closed chamber. The extracted, combined sample is passed to a collector, typically a molecule adsorber, which concentrates the chosen molecules by collection on a collecting surface. After the end of a collection period, the adsorbed molecules are released from the surface and passed to an identifier, such as an ion mobility spectrometer. By use of appropriate collection and valving elements, analysis can be accomplished quickly and accurately for a large number of luggage items or the like subject to examination.
U.S. Pat. No. 5,200,614 issued to Jenkins on Apr. 6, 1993, describes an ion mobility spectrometer which employs an electron capture process. A sample gas stream is irradiated to produce positive ions and electrons in an ionization chamber. An open grid electrode is employed in the ionization chamber to maintain a field-free space that claims to allow ion population to build up in the ionization chamber. However, a high electric field is periodically generated across the ionization chamber for periods of less than one millisecond to cause most ions of one polarity in the ionization chamber to be swept out and into a drift chamber. Ions of opposite polarity are discharge on the walls of the ionization chamber. The ions entering the drift chamber travel at drift velocities dependant on their respective charge and mass. A collector electrode is provided for sequentially collecting ions of differing mass, and the collected ion current is transmitted to a signal processing means for measuring intensity and arrival times for the collected ions. A potential can be maintained between the drift chamber and the ionization chamber for preventing ions from traveling down the drift chamber. However, this potential between the drift chamber and the ionization chamber may periodically be switched synchronously with the generation of the field across the ionization chamber to enable ions to pass into the drift chamber during the switching.
U.S. Pat. No. 5,457,316 issued to Cohen et al. on Oct. 10, 1995 relates to an ion mobility spectrometer sensor apparatus which is enclosed in a separate hermetically sealed housing, utilizing a drift gas for the determination of trace contaminants in a carrier gas, including a container for a sample gas containing an analyte the concentration of which is to be determined, means for purifying the sample gas to produce the carrier gas from it, the means for purifying being hermetically connected from the container through a metallic pipe, a source for the purified drift gas which may be the same or different than the carrier gas, an ion mobility spectrometer sensor having a carrier gas entrance and a drift gas entrance and a gas exit, the ion mobility spectrometer sensor being hermetically connected by a metallic pipe from the purifying means and from the source of the drift gas, a back diffusion trap is hermetically connected from the gas exit, and a signal readout is electrically and hermetically connected from the ion mobility spectrometer sensor for electrically sensing and displaying signals obtained in the sensor.
U.S. Pat. No. 6,606,899 issued to Ketkar et al. on Aug. 19, 2003 describes a device for measuring a total concentration of impurities in a sample gas which includes a housing having an inlet to allow the sample gas to enter the housing, an emitter to generate ions from the sample gas, a field gradient to accelerate the ions toward a collector, the collector adapted to measure total ions, and an outlet to allow the sample gas to exit the housing, whereby a change in total ions received by the collector indicates a change in the total concentration of impurities in the sample gas.
U.S. Pat. No. 6,924,479 issued to Blanchard Aug. 2, 2005 is directed to ion injection in a drift tube apparatus for mobility spectrometry without conventional ion shutters such as the Bradbury-Nielson or similar designs common to such drift tubes. Instead ions were passed between the ion source and drift region by using time-dependent electric field gradients that act as ion barriers between ordinary drift rings. Benefits of this design are simplicity and mechanical robustness. This ion injection technique dynamically accumulates the ions prior to their release into the drift region of the apparatus instead of destroying the ions created between shutter grid pulses, as does the Bradbury-Nielson method. The invention provides not only structural improvements to the well known drift tube apparatus, but also claims to provide inventive methods for operating a drift tube apparatus to achieve maximum analyte injection efficiency and improving ion detection sensitivity. Improving ion detection sensitivity of drift tubes has practical experimental application. Incorporation of the inventive apparatus into a smoke detector is a further practical application of the invention.
U.S. Pat. No. 6,828,795 issued to Krasnobaev et al on Dec. 7, 2004, is directed toward an explosive detection system which detects the presence of trace molecules in air. The sensitivity of such instruments is dependent on the concentration of target gas in the sample. The sampling efficiency can be greatly improved when the target object is warmed, even by only a few degrees. A directed emission of photons, typically infrared or visible light, can be used to significantly enhance vapor emission. The sensitivity of such instruments is also dependent on the method of gas sampling utilized. A cyclone sampling nozzle can greatly improve the sampling efficiency, particularly when the sampling needs to be performed at a distance from the air intake.
What is lacking in the prior art is a teaching of a combination of components which act in concert to provide a miniaturized handheld IMS device having enhanced sensitivity and performance for the detection of trace chemicals. Thus, if a highly sensitive and miniaturized Ion Mobility Spectrometer (IMS) could be produced, with demonstrated performance at elevated temperatures, a long felt need in the art would be met.